Lightning-arrester.



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LIGHTNING ARRESTER.

APPLICATION F|LED was. |909.

1 ,1 89,272. Patented July 4, 1916.

UNITED STATES PATENT GFFICE.

WILLIAM MOKEAN MCCLINTOCK, OF ST. PAUL, MINNESOTA.

LIGHTNING-ARRESTER.

Specification of Letters Patent.

Application led August 6, 1909. .Serial No. 511,617.

'a lightning arrester adapted particularlyfor the circuits of railway signaling devices and ,the object of the invention is to provide an arrester of simple, durable construction and one which will ground the heavy charge o1i` the line wires resulting from induction or other causes during a severe electrical storm.

The invention consists generally in a line circuit having terminals and a ground interposed between the terminals and provided with a block of carborunduin, which will allow only a slight leakage of a current of low voltage. but will becomel broken down and ground a current of high voltage such as would be induced during an electrical storm. 1

In' the accompanying drawings, forming part of this specification, Figure 1 is a lon-l gitudinal sectional view of a lightning airrester, embodying my invention, Fig. 2 -isf4 a side view of the same, Fig. 3 is a top view, Fig. 4 is a'side view of amodiied construction.

In the drawing, 2 represents a blockof insulating material and 3 and 4 binding,

screws having nuts 5 and 6 and forming the terminals of an electric circuit, a metallic plate 7 being interposed between the binding screws and closing the circuit between them.

8 is a third binding screw having nuts 9 and 10 and a plate 12 between which and the plate 7 an insulating ring 13 and a block 14 of carborundum material is arranged, the plate 12 being normally `insulated from the plate 7 against the passage of a curf rent of low voltage, such as would be generally used in the circuit of the signaling device.

A carborund'um block is irmly clamped The resistance of the carborundum block is suiiicient to prevent the passage of the normal current, but during an electrical storm when the air is heavily charged with electricity and currents of high voltage will be induced in the circuit, the carborundum block will become a conductor to such an extent that it will ground these high tension currents and prevent them from passing along the wires to the signaling-instrument. This carborundum block is molded by a suitable process, and is composed entirely of a conducting material, and is ofsuch a nature that it will oiier suiciently high resistance to prevent the grounding of a normal current but will ground a cur- 'l rent of high voltage, such as a bolt of lightning, and prevent such current from passing through the arrester to the instrument.

Patented July 4, 1916.

In Fig. 4 I have shown a modiied consize of the arrester and the purpose for which it is to be used.

The crystallized carborundum is broken up into grits of various grades which are separated by means of a screening process..

These grits are mixed with a small percentage of sodium silicate or other binding material, shaped in proper molds under 'ficiently high temperature to recrystallize the carboruiidum.

The particles of carborundum lie in close contact with one another in the block and being of' non-conducting material will resist the passage of a current of low voltage. lvlien, however, the arrester is subjected to abnormal conditions, as when the line is struck by a bolt of lightning, the particles of carborundum will lose their resistance to a Certain extent and will become a conductor for `a current of high voltage.

I claim as my invention: A lightning arrester comprising an insulating block, a conducting plate seated thereon, `a binding screw adapted for a ground connection mounted in said block and passing through said plate and insu. lated therefrom, a second conducting plate mounted on said binding screw and overhanging said first named plate and insulated therefrom, a block of high resistance material interposed between said conduct-4 ing. plates and in close contact therewith, said block having suiicient resistance to prevent the passage of a normal current therethrough but offering a decreased resistance to the `passage of a current of high 4voltage and forming temporarily a conduc- 

